The patron saint of Colli a Volturno is Saint Leonard the Abbot, protector of prisoners, while the co-patrons are Saint Anthony of Padua, Saint Antoninus and Saint Emygdius. His feast, on 6 November, includes both religious celebrations and the Antica Fiera di San Leonardo, with a display of local produce and craftsmanship.
The church dedicated to the saint, with a single nave and truncated apse, is the town's main church, distinct from the mother church of Santa Maria Assunta, the oldest in the historic centre, dating from roughly the start of the 11th century. The church of San Leonardo preserves 13th-century frescoes by Pietro Brunetto, decorating the dome with the Glory of God in Paradise and, in the choir, the Night and the Adoration of the Magi. A curious fact ties Colli to the history of medieval pilgrimages: drawing an ideal line between the Colli church and the abbey of San Leonardo in Lama Volara at Siponto, one of Christendom's most important waypoints for Western pilgrims heading to Jerusalem in the 12th century, one discovers that the two churches respect a perfect alignment on a west-east axis.
